WO 99/58836 (PTL 1) discloses a method for controlling a throttle valve in a gasoline engine including purge control means supplying evaporated fuel (gasoline vapor) to an intake system. In this control method, a throttle valve opening degree is corrected by changing an opening degree of the throttle valve in a closing direction in accordance with a calculated purge flow amount.
According to this control method, a vehicle speed does not change independently of a driver's intention, and drivability is improved (see PTL 1).